Arrays of acoustic transducers typically use elements with fixed beam patterns oriented in the un-steered direction of the array, as in the broadside direction of a planar array. Under steered conditions the source level will be less than the un-steered case if the array elements have a fixed beam pattern structure with maximum performance in the un-steered broadside direction. This is of particular note when a planar or line array is steered 90° from the broadside direction toward the end-fire direction. Another common problem associated with arrays of transducers is related to so-called grating or alias lobes where a side lobe is of the same source level as the main lobe, as in the case of small elements spaced one wavelength apart. Of particular interest is the typical array with center-to-center spacing of one half-wavelength which, if steered to end-fire, will also be automatically steered in the opposite direction. Quarter wavelength spacing with smaller array elements could be used to achieve single ended end-fire steering; however, in this case there could be less output as the array elements would be small and there could be interaction problems. These undesirable array steered conditions can be mitigated with the use of larger steered directional elements as described in this invention. As the center-to-center spacing is increased to one-half wavelength, the element size can be increased allowing the use of half as many transducer elements as in the case of the quarter wavelength spaced array.
Accordingly, it is an object of the present invention to provide an improved steered array source level and beam structure by use of steerable array elements.
Another object of the present invention is to provide unidirectional end-fire steering with half-wavelength center-to-center spaced steerable elements.
Another object of the present invention is to provide a steered acoustic transducer array with 360 degree coverage around a planar array.
Still another object of the present invention is a steerable modal vector projector transducer element with a small enough size for half wavelength array spacing at resonance.